Engineers working on the £1.5 million restoration of Netherton Tunnel showcased the scale of their task today.
Fears were raised that the 1.7 mile-long tunnel could collapse unless the essential maintenance works were carried out.
But now a four-month scheme is well under way to safeguard the future of the tunnel, which passes under Dudley town centre.
Engineers from construction firm May Gurney are working on the project alongside the waterways conservationists from the Canal and River Trust. The tunnel, running between Netherton and Tipton, is closed to narrowboats and walkers wanting to use the towpath in the meantime.
Canal and River Trust regional engineering manager John Ward said: “It is the nature of a 150-year-old structure that there will have to be ongoing repairs, and this is just one stage of them.”